Constellation for March 2024 –
Cancer
Cancer is an ancient constellation which represents the crab sent by Hera, the wife of Zeus, to defeat Hercules. Having been crushed underfoot by Heracles, it was then placed in the Heavens. However, it is almost impossible to make out in Havering as its brightest stars are Tarf which is magnitude 3.5 (despite being Beta Cancri) and Asellus Australis (Delta Cancri) which is 3.9; the other stars are fourth or fifth magnitude. Cancer is in fact the faintest of the twelve constellations which make up the Zodiac.
Cancer’s most famous object is the Beehive Cluster (Messier 44) [1], which is both large and bright. It can be seen with the naked eye in a darker area and it is easily spotted in binoculars. As well as being a beehive (because of its triangular shape), it was identified as a manger (feeding stall) in classical times, and its two attendant stars are known as Asellus Borealis and Asellus Australis (the Northern and Southern Asses). About 625 million years old, it is a relatively close 577 light years distant.
There is another, dimmer cluster in Cancer,
Messier 67 [2], which is two degrees to the west (right) of Acubens. It is one of the oldest clusters known, being between 3.2 and 5 billion years old, hence its surviving stars are like the Sun or red giants. M67 is 2,700 light years away from us and roughly the size of the full Moon.
Cancer has several nice doubles. Iota Cancri is similar to Albireo, being a fairly wide yellow and blue double, which are magnitude 4.1 and 6; it is sometimes called the winter or spring Albireo. Tegmine (Zeta Cancri) [3] is a tighter pairing of two yellow stars, mag. 4.9 and 5.9. One of my favourite doubles is Phi2 Cancri [4], which is an equal pair (mag. 6.2) of yellow-white stars which are fairly tight.
Just to the left (or east) of Iota Cancri is a pair of fairly bright stars: 53 Cancri, an orange red giant (mag. 6.5) and
55 Cancri, a yellow star (mag. 6.0) which is departing the main sequence, 277 arcseconds away; they can be split with binoculars. 55 Cancri, which is 41 light years distant, is of interest to astronomers as it has at least 5 exoplanets orbiting it. As a star with exoplanets, it has been named Copernicus by the IAU (having previously been known as Rho1 Cancri). Finally, there is Omicron Cancri [5], which is an extremely wide (976 arcseconds, just over 15 arcminutes) pair of white stars which are similar in brightness (mag. 5.4 and 5.7) and are a binary system despite the separation. It should be possible to split with the naked eye in a very dark area, but again it is easily split with binoculars.
